Flooding of ancient Salton Sea linked to San Andreas earthquakes

Then-Scripps graduate student Danny Brothers surveys sediments near Salton Sea in 2007. -  Scripps Institution of Oceanography, UC San Diego
Then-Scripps graduate student Danny Brothers surveys sediments near Salton Sea in 2007. – Scripps Institution of Oceanography, UC San Diego

Southern California’s Salton Sea, once a large natural lake fed by the Colorado River, may play an important role in the earthquake cycle of the southern San Andreas Fault and may have triggered large earthquakes in the past.

Researchers at Scripps Institution of Oceanography, UC San Diego, the U.S. Geological Survey (USGS) and the University of Nevada, Reno, discovered new faults in the Salton Sea near the southern end of the San Andreas Fault. By examining displacement indicators preserved in pristine sedimentary deposits, the team reconstructed their earthquake history and found evidence for coincident timing between flooding of the ancient Salton Sea and fault rupture. Rupture on these newly discovered “stepover” faults has the potential to trigger large earthquakes on the southern San Andreas Fault.

The report appears in the online version of the journal Nature Geoscience on June 26.

The Salton Sea covers a structural boundary at the southern end of the San Andreas Fault where it takes a southwestward step to the Imperial Fault. The region is closely monitored because the last large earthquake on this section of the San Andreas occurred approximately 300 years ago and the fault is considered by many experts to be overdue for another.

By imaging beneath the Salton Sea, the study identified the key role of stepover faults that run at an angle to the San Andreas Fault. The smaller faults rupture relatively frequently and, at times, they ruptured in concert with Colorado River flooding of the Salton Trough. Report lead author Danny Brothers said that this research does not improve the ability to predict such a quake but suggests that heightened preparedness for a major quake immediately following smaller quakes in the stepover zone is warranted.

“To fully understand the hazards and rupture scenarios associated with the southern San Andreas Fault, we can’t limit our study to the San Andreas Fault itself,” said Brothers, a researcher now at the USGS who conducted most of the research while a graduate student at Scripps. “These stepover zones really need to be considered when assessing earthquake hazards and need to be examined as potential triggers for destructive earthquakes on the larger faults.”

The current dimensions of the Salton Sea located in California’s Imperial Valley are but a fraction of the natural lake that preceded it. Through cycles of flooding and evaporation, the historical Lake Cahuilla was once one and a half times the size of Lake Tahoe at its maximum. What is left since the beginning of the 20th Century – when local authorities redirected the Colorado River away from the lake – is less than 1/25th that size.

When its natural dimensions were in place, Lake Cahuilla and its surrounding region experienced in a 1,000-year period five earthquakes on the Southern San Andreas that are believed to have been larger than magnitude 7. The temblors occurred about 180 years apart. It’s been more than 300 years since the last one. Diversion of the Colorado River and the lack of flooding events in the local basin known as the Salton Trough may be one possible explanation.

The researchers studied the sediments deposited over several millennia on the lake floor and found coincident timing between several flooding events and rupture of step-over faults, which in turn, may have loaded the San Andreas. Stress models showed that the predominantly normal faults with vertical displacement in the Salton Sea are more vulnerable to sudden increases in vertical loads caused by lake filling. Those failures may have triggered the movement of California’s primary fault in several instances, the researchers said. No such sequence has taken place since the lake assumed its current dimensions.

“We’ve been baffled as to why the Southern San Andreas hasn’t gone. It’s been compared to a woman who is 15 months pregnant,” said Scripps seismologist Debi Kilb, a report co-author. “Now this paper offers one explanation why.”

The researchers cautioned that failure of the stepover faults is ultimately driven by tectonic forces and could still set off a major rupture of the San Andreas Fault independently of any lake level fluctuations. Other research teams have estimated that stress buildup in the area is still great enough to produce a quake between magnitude 7 and 8. The idea that the San Andreas is triggered by stress loading in the Salton Sea supports the assumption by many scientists that a future quake sequence could propagate northward and potentially cause significant damage in the Los Angeles area.

“Earthquake simulations reveal that shaking of large metropolitan areas such as Riverside and Los Angeles will be larger if the earthquake propagates from south to north – our research suggests that the Salton Sea stepover zone may provide a trigger for such a propagation direction,” said Scripps geologist Neal Driscoll, a report co-author.

Brothers said that one of the most immediate applications of the research is as a guide to development in the Salton Sea region, which has been the subject of environmental restoration efforts in recent years.

“Large earthquakes on the southern San Andreas most likely will be accompanied by liquefaction in the Imperial Valley. In addition to ground shaking, the liquefaction will cause damage to water conveyance systems and existing infrastructure in the region and is likely to affect Salton Sea restoration efforts,” he said.

“Not only were we able to address seismic hazards issues along the San Andreas Fault, but this research also highlights the broader use and capabilities of new techniques and technologies to study hazards under bodies of water,” added Graham Kent, director of the Nevada Seismological Laboratory at the University of Nevada, Reno and a co-author of the report. “This can have application for other regions where the presence of water has left problems undetected.”

Ocean currents speed melting of Antarctic ice

Upwelling seawater along parts of Pine Island Glacier Ice Shelf has carved out caves in the ice and drawn wildlife like this whale. -  Maria Stenzel, all rights reserved.
Upwelling seawater along parts of Pine Island Glacier Ice Shelf has carved out caves in the ice and drawn wildlife like this whale. – Maria Stenzel, all rights reserved.

Stronger ocean currents beneath West Antarctica’s Pine Island Glacier Ice Shelf are eroding the ice from below, speeding the melting of the glacier as a whole, according to a new study in Nature Geoscience. A growing cavity beneath the ice shelf has allowed more warm water to melt the ice, the researchers say-a process that feeds back into the ongoing rise in global sea levels. The glacier is currently sliding into the sea at a clip of four kilometers (2.5 miles) a year, while its ice shelf is melting at about 80 cubic kilometers a year – 50 percent faster than it was in the early 1990s – the paper estimates.

“More warm water from the deep ocean is entering the cavity beneath the ice shelf, and it is warmest where the ice is thickest,” said study’s lead author, Stan Jacobs, an oceanographer at Columbia University’s Lamont-Doherty Earth Observatory.

In 2009, Jacobs and an international team of scientists sailed to the Amundsen Sea aboard the icebreaking ship Nathaniel B. Palmer to study the region’s thinning ice shelves-floating tongues of ice where landbound glaciers meet the sea. One goal was to study oceanic changes near the Pine Island Glacier Ice Shelf, which they had visited in an earlier expedition, in 1994. The researchers found that in 15 years, melting beneath the ice shelf had risen by about 50 percent. Although regional ocean temperatures had also warmed slightly, by 0.2 degrees C or so, that was not enough to account for the jump.

The local geology offered one explanation. On the same cruise, a group led by Adrian Jenkins, a researcher at British Antarctic Survey and study co-author, sent a robot submarine beneath the ice shelf, revealing an underwater ridge. The researchers surmised that the ridge had once slowed the glacier like a giant retaining wall. When the receding glacier detached from the ridge, sometime before the 1970s, the warm deep water gained access to deeper parts of the glacier. Over time, the inner cavity grew, more warm deep water flowed in, more melt water flowed out, and the ice thinned. With less friction between the ice shelf and seafloor, the landbound glacier behind it accelerated its slide into the sea. Other glaciers in the Amundsen region have also thinned or widened, including Thwaites Glacier and the much larger Getz Ice Shelf.

One day, near the southern edge of Pine Island Glacier Ice Shelf, the researchers directly observed the strength of the melting process as they watched frigid, seawater appear to boil on the surface like a kettle on the stove. To Jacobs, it suggested that deep water, buoyed by added fresh glacial melt, was rising to the surface in a process called upwelling. Jacobs had never witnessed upwelling first hand, but colleagues had described something similar in the fjords of Greenland, where summer runoff and melting glacier fronts can also drive buoyant plumes to the sea surface.

In recent decades, researchers have found evidence that Antarctica is getting windier, and this may also help explain the changes in ocean circulation. Stronger circumpolar winds would tend to push sea ice and surface water north, says Jacobs. That in turn, would allow more warm water from the deep ocean to upwell onto the Amundsen Sea’s continental shelf and into its ice shelf cavities.

Pine Island Glacier, among other ice streams in Antarctica, is being closely watched for its potential to redraw coastlines worldwide. Global sea levels are currently rising at about 3 millimeters (.12 inches) a year. By one estimate, the total collapse of Pine Island Glacier and its tributaries could raise sea level by 24 centimeters (9 inches).

The paper adds important and timely insights about oceanic changes in the region, says Eric Rignot, a professor at University of California at Irvine and a senior research scientist at NASA’s Jet Propulsion Laboratory. “The main reason the glaciers are thinning in this region, we think, is the presence of warm waters,” he said. “Warm waters did not get there because the ocean warmed up, but because of subtle changes in ocean circulation. Ocean circulation is key. This study reinforces this concept.”

Northern Eurasian snowpack could be a predictor of winter weather in US, team from UGA reports

Every winter, weather forecasters talk about the snow cover in the northern U.S. and into Canada as a factor in how deep the deep-freeze will be in the states. A new study by researchers at the University of Georgia indicates they may be looking, at least partially, in the wrong place.

It turns out that snow piling up over a band of frozen tundra from Siberia to far-northern Europe may have as much effect on the climate of the U.S. as the much-better-known El Niño and La Niña.

The new work, just published in the International Journal of Climatology, reports that to understand how cold (or warm) the winter season will be in the U.S., researchers and weather forecasters should also take a closer look at snowpack in northern Eurasia laid down the previous October and November.

“To date, there had been no thorough examination of how snow cover from various regions of Eurasia influences North American winter temperatures,” said climatologist Thomas Mote of UGA’s department of geography and leader of the research. “The goal of this research was to determine whether there is a significant relationship between autumn snow extent in specific regions of Eurasia and temperatures across North America during the subsequent winter.”

Co-author of the paper was Emily Kutney, a former graduate student in Mote’s lab who has since earned her master’s degree and left UGA.

While other scientists have postulated that snow cover on the Eurasian landmass has a strong effect on winters in North America, the new study is the first to narrow down the location of the area that causes the most direct effect on U.S. winters-an area in northwest Eurasia that includes part of Siberia-though the entire effective area extends as far west as northern Scandinavia.

“One difficulty in comparing previous studies is that they have used multiple definitions of Eurasian snow cover,” said Mote. “Our work looked at the role of various key areas of Eurasian snow cover on atmospheric circulation, including the systems called the Arctic Oscillation and the Pacific/North American teleconnection.”

The findings have new significance for seasonal climate outlooks, which predict whether upcoming seasons will be colder or warmer, or wetter or drier than normal. Years with extensive autumn snow in northwest Eurasia were associated with subsequent winter temperatures as much as seven degrees (Fahrenheit) lower near the center of North America. This difference is roughly the same as a one-month shift in climate.

Such information can be crucial for everything from agricultural to daily life in areas that normally have brutal winters. The crucial time to look at the snow cover in Eurasia is during October and November in order to understand the upcoming winters in North America, said Mote.

Even more complexity enters the system of interrelated climate phenomena when looking at the possibility that sea ice in the Atlantic and Arctic Oceans might affect Eurasian snow cover and thus winters in North America.

“It’s interesting, because it implies to us that the potential impact of this new idea could be as large or larger than El Niño and La Niña events,” said Mote.

The new study is more about seasonal climate predictions than short-term modeling for weather.

Mote also led a team that reported in 2008 a dramatic rise in the rate of melt in the ice sheet of Greenland. He and colleagues found that it was 60 percent higher in 2007 than ever before recorded. Mote used a nearly 40-year record of satellite data to discover the dramatic melting.

Stiff sediments made 2004 Sumatra earthquake deadliest in history

At a typical subduction zone, the fault ruptures primarily along the boundary between the two tectonic plates and dissipates in weak sediments (a), or ruptures along 'splay faults' (b); in either case, stopping far short of the trench. In the area of the 2004 Sumatra earthquake, sediments are thicker and stronger, extending the rupture closer to the trench for a larger earthquake and, due to deeper water, a much larger tsunami. -  UT Austin
At a typical subduction zone, the fault ruptures primarily along the boundary between the two tectonic plates and dissipates in weak sediments (a), or ruptures along ‘splay faults’ (b); in either case, stopping far short of the trench. In the area of the 2004 Sumatra earthquake, sediments are thicker and stronger, extending the rupture closer to the trench for a larger earthquake and, due to deeper water, a much larger tsunami. – UT Austin

An international team of geoscientists has discovered an unusual geological formation that helps explain how an undersea earthquake off the coast of Sumatra in December 2004 spawned the deadliest tsunami in recorded history.

Instead of the usual weak, loose sediments typically found above the type of geologic fault that caused the earthquake, the team found a thick plateau of hard, compacted sediments. Once the fault snapped, the rupture was able to spread from tens of kilometers below the seafloor to just a few kilometers below the seafloor, much farther than weak sediments would have permitted. The extra distance allowed it to move a larger column of seawater above it, unleashing much larger tsunami waves.

“The results suggest we should be concerned about locations with large thicknesses of sediments in the trench, especially those which have built marginal plateaus,” said Sean Gulick, research scientist at The University of Texas at Austin’s Institute for Geophysics. “These may promote more seaward rupture during great earthquakes and a more significant tsunami.”

The team’s results appear this week in an article lead-authored by Gulick in an advance online publication of the journal Nature Geoscience.

The team from The University of Texas at Austin, The University of Southampton in the United Kingdom, The Agency for the Assessment and Application of Technology in Indonesia and The Indonesia Institute for Sciences used seismic instruments, which emit sound waves, to visualize subsurface structures.

Early in the morning of Dec. 26, 2004 a powerful undersea earthquake started off the west coast of Sumatra, Indonesia. The resulting tsunami caused devastation along the coastlines bordering the Indian Ocean with tsunami waves up to 30 meters (100 feet) high inundating coastal communities. With very little warning of impending disaster, more than 230,000 people died and millions became homeless.

The earthquake struck along a fault where the Indo-Australian plate is being pushed beneath the Sunda plate to the east. This is known as a subduction zone and in this case the plates meet at the Sunda Trench, around 300km west of Sumatra. The Indo-Australian plate normally moves slowly under the Sunda plate, but when the rupture occurred, it violently surged forward.

The Sunda Trench is full of ancient sediment, some of which has washed out of the Ganges over millions of years forming a massive accumulation of sedimentary rock called the Nicobar Fan. As the Indo-Australian plate is subducted, these sediments are scraped off to form what’s called an accretionary prism. Usually an accretionary prism slopes consistently away from the trench, but here the seabed shallows steeply before flattening out, forming a plateau.

Subduction earthquakes are thought to start tens of kilometers beneath the Earth’s surface. Displacement or “slip” on the fault, as geologists call it, propagates upwards and generally dissipates as it reaches weaker rocks closer to the surface. If it were an ordinary seismic zone, the sediment in the Sunda Trench should have slowed the upward and westward journey of the 2004 earthquake, generating a tsunami in the shallower water on the landward (east) side of the trench.

But in fact the fault slip seems to have reached close to the trench, lifting large sections of the seabed in deeper water and producing a much larger tsunami.

This latest report extends work published last year in the journal Science that found a number of unusual features at the rupture zone of the 2004 earthquake such as the seabed topography, how the sediments are deformed and the locations of small earthquakes (aftershocks) following the main earthquake. The researchers also reported then that the fault zone was a much lower density zone than surrounding sediments, perhaps reducing friction and allowing a larger slip.

Electrical water detection

A quick and easy way to detect groundwater in semi-arid hard rock areas that is also economical could improve the siting of borewells to improve clean water supply in the developing world. Details of the approach are outlined in the International Journal of Hydrology Science and Technology this month.

P.D. Sreedevi, Dewashish Kumar and Shakeel Ahmed National Geophysical Research Institute in Hyderabad, India, explain how electrical conductivity (EC) logs of hard rock terrain recorded before and after the monsoon season can reveal differences that show where water accumulates most in subterranean rock fissures. By comparing the data with other geological measurements and drilling experiments, the team is available to correlate the EC data with regions of underground water without additional test drilling.

Understanding hard rock aquifers relies on hydrology of fractured rock and knowing details of the subterranean environment. Data is commonly obtained through drilling test boreholes or investigating underground openings. Such work is hazardous and time consuming and does not necessarily reveal the most appropriate site to sink a water well. However, anomalies in electrical conductivity measurements of which many have been made in various regions might be useful in finding the most abundant sources of groundwater.

The researchers demonstrated how effective the approach might be in correlating information from 25 boreholes in the Maheshwaram watershed situated in the Ranga Reddy district of Andhra Pradesh, India, about 30 kilometers south of Hyderabad, covering an area of about 60 square kilometers. The area is semi-arid with average annual rainfall of 750 millimeters. The bedrock is mostly granite. The team points out that, based on the detailed geological and hydrogeological studies, the aquifer is classified as a two-tier coupled system with weathered and fractured layers that exist over almost the entire area. However, due to over-exploitation, the groundwater levels have affected the weathered layers and groundwater flow is currently in the fractured rock aquifer. There are no rivers feeding the aquifers so the system relies on the monsoon to for replenishment.

“Our approach is fast and cost effective and could be very useful as a screening tool prior to conducting hydraulic testing and water sampling,” the team concludes.

Geoscience from the Archean to the Anthropocene converges in Minneapolis

Registration is open for the Geological Society of America’s (GSA’s) 123rd Annual Meeting and Exhibition, to be held 9-12 October 2011 at the Minneapolis Convention Center in Minneapolis, Minnesota, USA. Minneapolis has not hosted the GSA meeting since 1972, and the 2011 Midwest meeting is shaping up to be one of GSA’s largest! Find complete meeting information at http://www.geosociety.org/meetings/2011/ or browse the June Annual Meeting issue of GSA Today at http://www.geosociety.org/gsatoday/archive/21/6/.

“This year’s theme, Archean to Anthropocene, the past is the key to the future, captures the broad research and education agenda of the GSA community as a whole, as well as the application of our work to society,” says Harvey Thorleifson, Minnesota State Geologist and GSA’s Local Planning Committee Chair. “Recent escalation of the visibility of the Anthropocene concept illustrates the scientific relevance of the meeting, and our program will provide an opportunity for participants to make contact with and reflect on current influential thinking on this topic.”

Representatives of the media are cordially invited to attend and participate in technical sessions, field trips, and other special events. Eligible media personnel receive complimentary registration and are invited to use GSA’s Newsroom facilities while covering the meeting. Review eligibility requirements and access media registration at http://www.geosociety.org/meetings/2011/rMedia.htm.

Public information officers from universities, government agencies, and research institutions are also invited to take advantage of complimentary registration at the GSA Annual Meeting to distribute press releases on presentations by their scientists and meet with media onsite.

Contact Christa Stratton at the address above for more information or assistance with media registration (http://www.geosociety.org/meetings/2011/rMedia.htm). Program highlights follow.

*** SCIENTIFIC PROGRAM ***


Technical Sessions run Sunday-Wednesday, 8 a.m.𔃃:30 p.m. All sessions will take place at the Minneapolis Convention Center, 1301 Second Avenue South, Minneapolis, Minnesota 55403, USA.

Posters will be on display 9 a.m.𔃄 p.m. Authors will be present either 9󈝷 a.m. or 2𔃂 p.m. and are encouraged to be at their posters during the 4:30𔃄 p.m. beer reception as well.

8 Pardee Keynote Symposia: Descriptions at http://www.geosociety.org/meetings/2011/sessions/pardee.htm.

The Frontiers of Quaternary Geochronology: Extension or Overextension of Dating Methods for Quaternary Geology and Geomorphology?

Sun., 9 Oct.: 8 a.m.-noon

Honoring British Geologist Arthur Holmes (1890�) for Contributions to Geochronology, Plate Tectonics, and the Origin of Granite

Sun., 9 Oct.: 1:30𔃃:30 p.m.

Exploration of the Deep Biosphere

Mon., 10 Oct.: 8-noon

Rare Earth Elements and Critical Minerals for a Sustainable and Secure Future

Mon., 10 Oct.: 1:30𔃃:30 p.m.

The EarthScope Program: Recent Results and Future Projects

Tue., 11 Oct.: 8 a.m.-noon

Prairie Ice Streams

Tue., 11 Oct.: 1:30𔃃:30 p.m.

Earth’s Early Atmosphere and Surface Environment

Wed., 12 Oct.: 8 a.m.-noon

Global Water Sustainability

Wed., 12 Oct.: 1:30𔃃:30 p.m.

5 Special Sessions: http://www.geosociety.org/meetings/2011/sessions/special.htm</A

GSA Geophysics Division 40th Anniversary Special Session

Highlights major scientific discoveries concerning the lithosphere, from top to bottom. The last talk will be given by the 2011 George P. Woollard award winner, William A. DiMichele.

The Past Yucca Mountain Project-Advancing Science and Technology for the Future: Was It Worth the Cost?

During the life of the program (1988�), approximately $1.1B was spent on scientific and technical investigations across a range of disciplines. This symposium reviews the innovative work conducted by program investigators and transfer of those technologies to the wider scientific community.

Crossing the Digital Divide: Availability of Geoscience Knowledge for Resolving Environmental and Societal Challenges

This special session addresses the entire digital geoscience data collection, management, and dissemination process.

Planetary Geology Division 30th Anniversary-Then and Now: The Past 30 Years of Solar System Exploration

A retrospective on the major advances in understanding the geologic histories of planets and moons over the past 30 years.

Water and Sediment Dynamics in Agricultural Landscapes: Toward Prediction of Watershed Sediment Yield

This session brings together geographers, geomorphologists, hydrologists, soil scientists, and agricultural scientists to evaluate approaches for predicting water and sediment yield in agricultural landscapes.

217 Topical Sessions: http://www.geosociety.org/meetings/2011/sessions/topical.asp.

(Search by discipline categories or sponsors from the drop-down menus, or use your browser’s “find” feature to search for keywords or convener names.)

Discipline Sessions: http://www.geosociety.org/meetings/2011/jtpc.htm

Petroleum has been added as the newest of 29 general discipline session categories this year.

More complete technical program information will be available after the abstract submission deadline: 26 July 2011.

Field Trips



Early October is prime field season in the upper Midwest. A diverse slate of 45 field trips span a geologically broad range of topics, including the Precambrian geology of the southern Canadian Shield; the economic geology of the Lake Superior region; Phanerozoic strata in Minnesota, Wisconsin, Iowa, and North Dakota; glacial geology; hydrogeology and limnology; undergraduate and K󈝸 geoscience field education; the geology and hydrology of the Twin Cities metro area; geology by bicycle; terroir; geoarchaeology; biogeohydrochemistry; and tours of area research labs and vessels.

Find information on pre-meeting, concurrent, and post-meeting field trips at http://www.geosociety.org/meetings/2011/fieldTrips.htm. Members of the media must pay for field trips in which they wish to participate.

*** HELPFUL TRAVEL LINKS ***


For best selection, book lodging early at http://www.geosociety.org/meetings/2011/lodging.htm.

International journalists: Find visa information at http://www.geosociety.org/meetings/2011/visa.htm.

Find more information about Minneapolis at http://minneapolisconventioncenter.com/public/.

Penn researchers link fastest sea-level rise in 2 millennia to increasing temperatures

An international research team including University of Pennsylvania scientists has shown that the rate of sea-level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years and that there is a consistent link between changes in global mean surface temperature and sea level.

The research was conducted by members of the Department of Earth and Environmental Science in Penn’s School of Arts and Science: Benjamin Horton, associate professor and director of the Sea Level Research Laboratory, and postdoctoral fellow Andrew Kemp, now at Yale University’s Climate and Energy Institute.

Their work will be published in the journal Proceedings of the National Academy of Sciences on June 20.

“Sea-level rise is a potentially disastrous outcome of climate change, as rising temperatures melt land-based ice and warm ocean waters,” Horton said.

“Scenarios of future rise are dependent upon understanding the response of sea level to climate changes. Accurate estimates of past sea-level variability provide a context for such projections,” Kemp said.

In the new study, researchers provided the first continuous sea-level reconstruction for the past 2,000 years and compared variations in global temperature to changes in sea level during this time period.

The team found that sea level was relatively stable from 200 B.C. to 1,000 A.D. During a warm climate period beginning in the 11th century known as the Medieval Climate Anomaly, sea level rose by about half a millimeter per year for 400 years. There was then a second period of stable sea level associated with a cooler period, known as the Little Ice Age, which persisted until the late 19th century. Since the late 19th century, however, sea level has risen by more than 2 millimeters per year on average, which is the steepest rate for more than 2,100 years.

To reconstruct sea level, the research team used microfossils called foraminifera preserved in sediment cores from coastal salt marshes in North Carolina. The age of these cores was estimated using radiocarbon dating and several complementary techniques.

To ensure the validity of their approach, the team members confirmed their reconstructions against tide-gauge measurements from North Carolina for the past 80 years and global tide-gauge records for the past 300 years. A second reconstruction from Massachusetts confirmed their findings. The records were also corrected for contributions to sea-level rise made by vertical land movements.

The team’s research shows that the reconstructed changes in sea level during the past millennium are consistent with past global temperatures and can be described using a model relating the rate of sea-level rise to global temperature.

“The data from the past help to calibrate our model and will improve sea-level rise projections under scenarios of future temperature rise,” research team member Stefan Rahmstorf said.

Atmospheric carbon dioxide buildup unlikely to spark abrupt climate change

There have been instances in Earth history when average temperatures have changed rapidly, as much as 10 degrees Celsius (18 degrees Fahrenheit) over a few decades, and some have speculated the same could happen again as the atmosphere becomes overloaded with carbon dioxide.

New research lends support to evidence from numerous recent studies that suggest abrupt climate change appears to be the result of alterations in ocean circulation uniquely associated with ice ages.

“There might be other mechanisms by which greenhouse gases may cause an abrupt climate change, but we know of no such mechanism from the geological record,” said David Battisti, a University of Washington atmospheric sciences professor.

Battisti was part of a team that used a numerical climate model coupled with an oxygen-isotope model to determine what caused climate shifts in a computer-generated episode that mimicked Heinrich events during the last ice age, from 110,000 to 10,000 years ago. Heinrich events produced huge numbers of North Atlantic Ocean icebergs that had broken off from glaciers.

The simulations showed the sudden increase in North Atlantic sea ice cooled the Northern Hemisphere, including the surface of the Indian Ocean, which reduced rainfall over India and weakened the Indian monsoon.

Battisti noted that while carbon dioxide-induced climate change is unlikely to be abrupt, the impacts of changing climate could be.

“When you lose a keystone species, ecosystems can change very rapidly,” he said. “Smoothly retreating sea ice will cause fast warming if you live within a thousand kilometers of the ice. If warming slowly dries already semi-arid places, fires are going to be more likely.”

Previous studies of carbonate deposits from caves in China and India are believed to show the intensity of monsoon precipitation through the ratio of specific oxygen isotopes. The modeling the scientists’ used in the current study reproduced those isotope ratios, and they determined that the Heinrich events were associated with changes in the intensity of monsoon rainfall in India rather than East Asia.

What will climate change and sea level rise mean for barrier islands?

The Advanced Land Imager on NASA's Earth Observing-1 satellite captured this image of a barrier island facing the Beaufort Sea, on the northern edge of Canada's Northwest Territories. The overall thawing of Arctic climates, as well as increasing sea level rise, has caused barrier island shorelines in this region to erode more rapidly than elsewhere in the world. -  (Credit: NASA's Earth Observatory)
The Advanced Land Imager on NASA’s Earth Observing-1 satellite captured this image of a barrier island facing the Beaufort Sea, on the northern edge of Canada’s Northwest Territories. The overall thawing of Arctic climates, as well as increasing sea level rise, has caused barrier island shorelines in this region to erode more rapidly than elsewhere in the world. – (Credit: NASA’s Earth Observatory)

A new survey of barrier islands published earlier this spring offers the most thorough assessment to date of the thousands of small islands that hug the coasts of the world’s landmasses. The study, led by Matthew Stutz of Meredith College, Raleigh, N.C., and Orrin Pilkey of Duke University, Durham, N.C., offers new insight into how the islands form and evolve over time – and how they may fare as the climate changes and sea level rises.

The survey is based on a global collection of satellite images from Landsat 7 as well as information from topographic and navigational charts. The satellite images were captured in 2000, and processed by a private company as part of an effort funded by NASA and the U.S. Geological Survey.

During the 20th century, sea level has risen by an average of 1.7 millimeters (about 1/16 of an inch) per year. Since 1993, NASA satellites have observed an average sea level rise of 3.27 millimeters (about 1/8 of an inch) per year. A better understanding of how climate change and sea level rise are shaping barrier islands will also lead to a more complete grasp of how these dynamic forces are affecting more populated coastal areas.

Stutz, the study’s lead author, highlighted a series of key findings from the new survey during an interview with a NASA science writer.

Every barrier island is unique.

Every island chain has a complex set of forces acting on it that underpin how islands form and how they’re likely to change over time. Barrier islands often develop in the mouths of flooded river valleys as sea level rises, but they can also form at the end of rivers as sediment builds up and creates a delta. Other important factors in barrier island formation include regional tectonics, sea level changes, climate, vegetation and wave activity. “Understanding how such forces impact barrier islands is the key to understanding how climate change will affect our coastlines,” noted Stutz.

Sea level rise can eliminate — or create — barrier islands.

Scientists estimate that the rate of sea level rise will likely double or triple in the next hundred years due to climate change. Paradoxically, gradual sea level rise can generate new barrier islands. Rising seas create shallow bays that develop barrier islands in the mouths of the bays along certain types of coastline.

Stutz’s analysis found rising sea level in the last 5,000 years is associated with the greatest barrier island abundance, especially in the North Atlantic and Arctic. Stable or falling sea level, meanwhile, a pattern more typical of the Southern Hemisphere in the last 5,000 years, has produced fewer islands and a higher percentage of islands along river deltas.

However, extremely rapid sea level rise — especially when coupled with decreases in sediment supply — can simply inundate islands causing them to break up and disappear. Islands are eroding rapidly along the Mississippi Delta, Eastern Canada and the Arctic for these reasons.

“However, rising sea level is not just like pouring more water into a bathtub,” Stutz emphasized. Islands react differently based on the geology in a region and how the waves and tides in an area are affected. People tend to assume sea level rise means fewer islands no matter what, but the rate of rise is critical.”

There are far more barrier islands than previously thought.

A survey conducted by the same researchers tallied 1,492 barrier islands in 2001, but Stutz and Pilkey counted more than 2,149 this time. The difference: the researchers had access to higher-quality satellite imagery that covered a larger portion of the globe than they did last time. “It’s not that 657 islands appeared overnight. We simply did a more thorough job of counting what was already out there,” said Stutz. The researchers counted extensive island chains in Brazil, Madagascar and Australia that the previous survey had left out.

Barrier islands cluster along tectonically calm coasts.

Stable coasts, such as the eastern coast of the United States, tend to have wide, low relief areas with shallow estuaries that are conducive to barrier island formation. In contrast, continental margins near actively colliding plates, which generate earthquakes and volcanoes, produce fewer barrier islands. At active margins, such as the rocky cliffs along the Pacific, steep grades typically dominate coastal areas and prevent the formation of islands.

Northern and Southern hemisphere islands differ.

The Northern Hemisphere is home to the majority — 74 percent — of barrier islands. That’s not surprising because the Northern Hemisphere contains about the same proportion of land. A less intuitive insight: the majority of Northern Hemisphere islands are in high-latitude Arctic or temperate climate zones, while most Southern Hemisphere islands are tropical. Why the discrepancy? Relative sea levels have fallen slowly in much of the Southern Hemisphere for the last 5,000 years, but the opposite has happened in the Arctic.

Storms are key molders of barrier island shape.

Storms tend to cause islands to retreat, carve new inlets that make them shorter and more numerous, and sometimes destroy them completely. The frequency of storms varies by latitude and climate. The Arctic and most temperate coasts experience regular storms, while more tropical areas experience few storms and more gentle swells most of the year, conditions that encourage the formation of sandy beaches. Major storms can cause drastic changes to barrier islands. After Hurricane Katrina, for example, many islands in the Mississippi River Delta were destroyed or radically changed.

Arctic barrier islands are retreating the fastest.

Barriers islands in the Arctic make up nearly a quarter of the world’s barrier islands, and they’re more vulnerable to climate change than islands anywhere else in the world. The reason: melting of sea ice and the permafrost that buffers Arctic islands from waves have left them susceptible to constant pounding from storms. Recently measured erosion rates in the Beaufort Sea show Arctic barrier islands eroding three to four times faster than islands in the continental United States. Any further acceleration in erosion rates could result in the rapid breakup of many Arctic islands, Stutz’s analysis noted.

More research is needed, especially on a local scale.

Coastal areas will likely experience major changes in sea levels this century due to climate change. The shifts, however, will be anything but uniform. NASA research shows that some coasts are experiencing sea level rise significantly faster than the global average of 3.27 millimeters (about 1/8 of an inch) per year, while other areas are experiencing slower rates of rise and even falling sea levels. “It would be nice if we could say we can predict exactly how a given island or island chain will react to rising sea levels or some other environmental change, but we’re simply not there yet for most islands, especially for many tropical islands where research dollars are scarce. We’re still a long way from being able to accurately model how an individual island will change as a result of climate change or even simple development pressure,” said Stutz.

How is the Arctic Ocean changing?

On Wednesday, 15 June, the research vessel Polarstern of the German Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association set off on its 26th arctic expedition. Over 130 scientists from research institutions in six countries will take part in three legs of the voyage. First of all, at long-term stations oceanographers and biologists will investigate how oceanic currents as well as the animal and plant world are changing between Spitsbergen and Greenland. Beginning in August, physical, biological and chemical changes in the central Arctic will be recorded. RV Polarstern is expected back in Bremerhaven on 7 October.

In the Fram Strait between Spitsbergen and Greenland oceanographic measuring devices have been continuously recording temperature, salt concentration, flow speed and direction for 14 years. Moorings with the sensors that have to be replaced after one or two years extend down to a depth of over 2,500 metres. To supplement these stationary measurements, a free-floating device will now be additionally employed for three months. The so-called Seaglider submerges down to a depth of 1,000 metres along its course line in order to carry out measurements. In between it regularly returns to the surface, transmits the data via satellite and receives new position coordinates. The recorded data show how the exchange of water masses and heat changes between the Arctic Ocean and the North Atlantic. The Fram Strait is the only deepwater connection between the two marine areas and therefore permits conclusions regarding the influence of the polar marine regions on the global ocean.

The second area under study is the so-called AWI HAUSGARTEN. It is the northernmost of ten observatories altogether in the European network ESONET (European Seafloor Observatory Network). Using this deep-sea long-term observatory of the Alfred Wegener Institute, biologists want to examine how communities of organisms in the open water and on the bottom of the deep sea react to the progressive warming of the nordic seas. In this context they will investigate the critical physiological and ecological limits of selected species. This makes it possible to draw conclusions as to whether organisms are able to tolerate increasing temperatures, for example, or whether they withdraw from the region as warming progresses. With the help of a remotely operated vehicle (ROV) chartered from the IFM-GEOMAR marine research institute in Kiel experiments will also be conducted on the floor of the deep sea. Another underwater vehicle (AUV), which has a length of around five metres, is also unmanned, but operates autonomously, will be used at water depths down to approx. 600 metres as well as just under the Arctic sea ice. By means of measuring instruments that were newly developed at the Alfred Wegener Institute, it records, among other things, the distribution of unicellular algae and the carbon dioxide concentration near the water surface. Furthermore, the scientists plan to take seafloor samples from a marine area in which fishery echosounders recently detected numerous gas flares. They indicate that probably enormous quantities of methane, a greenhouse gas with certain relevance for the climate, are released from the seafloor at water depths of around 400 metres west of Svalbard.

As of the beginning of August, the research vessel Polarstern will then set course for the Arctic Ocean. The focus will be on physical, biological and chemical changes in the central Arctic. The reduction of sea ice and the variability of ocean circulation and its heat and fresh water budgets are tightly linked with changes in the gas exchange as well as with biogeochemical and ecosystem processes in the sea ice and in the entire water column. To understand these interrelations better, the members of the expedition will take water and ice samples from the shallow Eurasian shelf seas all the way to the deep Canadian Basin and from the open sea to the pack ice. In addition, the researchers will install measuring devices that drift through the Arctic Ocean on ice floes for months and thus supply valuable data from this not easily accessible region. They then transmit these data to land via satellite. A subsequent comparison of the data to measurements from previous expeditions may indicate how the climate is changing in the Arctic. To continuously monitor the further progress of the changes, the researchers will moor measuring devices and sample-taking equipment, which will be picked up during another expedition to this marine region in the coming year.